I think it's too early to say, because the impact of work is seen over time.<p>But candidates probably include Breiman/Cutler for Random Forests, Dean/Ghemawat for MapReduce, Peter Shor for Shor's algorithm, Daphne Koller for machine learning, Jon Kleinberg for network algorithms, Luis von Ahn for human computation.
A couple of obvious exceptions are John Carmack (for 3D graphics algorithm design) and Linus Torvalds (for OS design), although whether or not they contributed to 'computer science' rather than their particular software domain is debatable.
The word "pioneer" refers to contributions at the <i>birth</i> of a field. CS is now an established field, there are no more "pioneers" in the sense that there are no longer "pioneers" discovering America by crossing oceans.<p>There are certainly "pioneers" operating today in sub-domains of CS: in machine learning, artificial intelligence, in parallelization, networking, cryptocurrency etc.<p>(and countless other fields related to or derived from CS).